Callisto is an enormous bear that resides south of the Demonic Ruins, and is the only monster to drop the tyrannical ring. He attacks using melee. He can knock players back a few tiles, which renders them unable to move for a few seconds, as well as heal himself slightly. He is also able to perform a deadly shockwave attack that can hit up to 60, and may combine this with a melee attack, which is capable of instantly killing the player if they are within melee range and do not have Protect from Melee active.

Callisto is immune to Magic damage, although spells with effects such as Vulnerability will still affect him.

↑ 1.01.1Jagex. Mod Ash's Twitter account. 9 Jun 2017. (Archived from the original on 2019-02-19.) Mod Ash: "I've re-run the numbers. Looks like 1/171 for all three of them. But the dragon 2h is 1/256 from them all."

There is a pile of bear droppings in the woods south of his spawn, with the examine text "Now you know." — a reference to the popular colloquialism, "Does a bear shit in the woods?", a rhetorical question in response to something where the answer is obviously yes.